ReviewSkeletal muscle imaging in neuromuscular disease
Introduction
The evaluation of a patient with a suspected neuromuscular disease relies on a combination of clinical history, physical examination, and ancillary testing, often including electrodiagnostic evaluation. With advances in the quality and availability of radiologic technology, imaging of muscles has a growing role in the evaluation of patients with suspected neuromuscular disorders. Muscle imaging often detects abnormalities suspected based on the physical exam but can also identify unsuspected pathologies. Muscle imaging can be used to screen multiple muscles to identify the presence and pattern of pathology to either inform the differential diagnosis directly or to direct the electrodiagnostic evaluation or muscle biopsy.
Muscle imaging is most commonly performed using MRI or ultrasound. Both MRI and ultrasound are painless, radiation-free modalities to identify neuromuscular pathology. Ultrasound can be obtained by the examiner at the bedside in the clinic setting and dynamic features of muscle can be explored. MRI allows for better imaging of deep structures and by applying different sequences can distinguish water and fat based pathologies.
Both MRI and ultrasound are used more commonly than either X-ray or CT scanning. X-rays are suboptimal for detecting most neuromuscular pathologies but can detect skeletal abnormalities and intramuscular calcifications. CT scan of muscle can detect fatty degeneration and atrophy characteristic of some myopathies or chronic denervation. Both X-ray and CT scans expose the patient to radiation without much advantage over MRI or ultrasound in the diagnosis and evaluation of neuromuscular disease. This article will therefore focus on ultrasound and MRI imaging of skeletal muscle.
Section snippets
Muscle ultrasound
Ultrasound has well recognized advantages of being a painless imaging modality that can be quickly applied at the bedside. The current availability of portable systems that are capable of providing good-quality high-resolution images has brought about a major shift in the application of imaging in the neuromuscular clinic from clinician-requested to clinician-directed. Specifically, the same clinician responsible for the clinical and neurophysiological diagnosis increasingly performs the
Muscle MRI
Muscle MRI compensates for its lack of convenience by the structural detail provided and the availability of specialized sequences to more precisely delineate the nature of the pathologic process.
T1-weighted MRI sequences produce high-resolution anatomical images of the muscle. Fat is bright on T1-weighted MRI, and as such are ideal to demonstrate the fatty replacement of muscle characteristic of many myopathies (Fig. 3B). T1-weighted MRI sequences will not give an indication of inflammation or
Quantitative muscle imaging
Quantitative imaging assessments of muscle, provides improved reliability and sensitivity for neuromuscular disease and allows for measurement of the degree of muscle pathology. Muscle imaging as a surrogate measure of disease activity is appealing for studying patients who are too young or too weak to participate in assessments based on strength and function but must also be sensitive enough to detect the slow progression seen in many neuromuscular disorders over time. Quantification of muscle
Imaging of specific neuromuscular disorders
Many myopathies have characteristic and highly selective patterns of muscle involvement [58], [59], [60]. A combination of history, physical exam, histopathology and increasingly, genetic testing will be sufficient to determine the diagnosis. In some patients, identifying the pattern of muscle involvement may help with the diagnostic process, such as improving diagnostic confidence, refining genetic testing, or in selecting appropriate sites for biopsy. The clinical examination is sometimes
Conclusions
This review highlights the practical applications of skeletal muscle imaging in neuromuscular disease. Qualitative and quantitative ultrasound and MRI techniques have a defined role in the diagnosis of muscle injury, including identifying evidence of muscle denervation and myopathy, delineating patterns of muscle involvement in hereditary myopathies, and optimizing muscle selection for biopsy. Further, quantitative imaging techniques may provide objective measures to evaluate disease
Conflicts of Interest/Disclosures
The authors declare that they have no financial or other conflicts of interest in relation to this research and its publication.
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